Philip-
Yes,
Hawaii does get some international bird migrants. Some of these are the
same sorts of international 'travellers' that we get here. Wandering
Tattlers for example. Perhaps in Australia, there exists some local
tolerance of the potential diseases that regular international migrants
carry. If they have been migrating here for x thousands of years, this may
have occurred. House Crows are not 'natural' migrants, and it is perhaps
possible that they may carry something (parasite or pathogen) which local birds
cannot tolerate. Correct me if I am wrong, but it seems likely that the
air sac mites threatening Gould's Finches had their origins in exotic cage
birds. I do not think that disease or pathogens can be entirely disounted
as a risk. Given the stresses placed on many native species by removal or
alteration of habitat, a newly arrived exotic disease may be the additional
factor that tips the balance towards decline.
Scott
O'Keeffe
A fair point, however Australia as a continent
that gets a large number of international bird migrants is not so likely to
suffer ill effects from that cause. The bird fauna here has probably long been
exposed to most such nasties. Hawaii, which is a tiny set of isolated islands
is in a different situation, smaller gene pool of virtually all species, so
probably less resistance and - well I don't know - does Hawaii get
international bird migrants?
